And while Sleeping Beauty was woken by a prince’s kiss, Helen knows her own story is unlikely to have a happy ending.

“At least in the fairytale she got to wake from her sleep,” she says.

“I go through life either sleeping or feeling like I’m sleepwalking. I’ve missed all the important moments of my life.

“I don’t have a social life; I don’t have a love life. With this illness you don’t live, you just exist.”

Winner: But Helen even felt tired as a child

Helen has Kleine-Levin Syndrome – dubbed Sleeping Beauty Syndrome – which has no known cure and affects just 1,000 known sufferers worldwide.

It leaves her exhausted and in constant agony, unable to do anything more than struggle to the sofa in the little time she is able to stay awake.

The condition is also believed to have affected her long-term memory.

When Helen flicks through the family album she has no recollection of the holidays, birthdays and Christmases when she was pictured smiling for the camera.

She cannot remember her first day at school or her first kiss.

And now she is incapable of doing anything to build new memories for the future.

She recently had to give up her job as a mortgage manager due to her condition, and now spends her days at home where she lives alone with her two dogs.

Too exhausted to do anything more than watch TV for a couple of hours before dozing off again, she rarely goes out more than once a month and depends on her mum to shop for her.

After sleeping for 21 hours Helen struggles to wake, and for that she relies on black Labrador Sooty and rottweiler Barney.

Memory loss: She can't remember her first day at school

Sooty will nudge her arm to wake her, and if she is still sleeping after an hour of this, 12-stone Barney barks into her face – rousing her from sleep with a noise Helen likens to that of a pneumatic drill.

Once awake, it can take from 10 minutes to an hour for Helen to properly open her eyes and for her limbs to become fully mobile, because her muscles become stiff and painful while she sleeps.

Helen says: “My body is often so stiff and exhausted I can’t do the washing up, let alone socialise.

“Some days I just lie on the sofa because my muscles are so sore. I can’t even go out to celebrate my mum’s birthday next month because it will be too exhausting.”

She often has to lean on Barney to support her aching limbs as she walks around her bungalow in Aberporth in South Wales.

Helen was finally diagnosed four years ago, but she knew from a young age that something was wrong. Her entire childhood was blighted by exhaustion, with people assuming she was lazy and stupid. She recalls: “One of my only childhood memories is going to a restaurant with my family and I was exhausted.

“I was looking at the menu and tried to ask what type of fish they were serving. But I was so tired I couldn’t get my words out properly and asked, ‘what is a fish?’

“Before I could correct myself, my family started laughing at me and it became a joke that ran for years.”

As a teenager, while her schoolmates spent the summer holidays going to parties and playing outdoors, Helen would spend the whole six-week break asleep, waking only to eat, drink and go to the toilet.

Tragic: No one know she was ill

She says: “Looking back on my youth is like watching snippets from a film, fast-forwarding huge sections in between.

“I knew back then there was something wrong with me, but nobody knew about Sleeping Beauty Syndrome in the 1980s. They just called it ‘daydreaming’.”

In spite of her struggles, Helen graduated from university and landed a good job.

But in February 2009 she caught flu and slept for three-and-a-half weeks before her family managed to wake her.

Over the next 18 months Helen underwent tests for everything from narcolepsy to various infections. She was misdiagnosed with depression and prescribed antidepressants. But in 2010 she was finally told she had KLS.

Tests showed Helen falls into a deep sleep in under five minutes – for an average sleeper this usually takes up to two hours.

She says: “Finally receiving a diagnosis was a relief.

“Doctors told me I could use medication to control it, but the condition will continue to get worse.”

Helen did not turn to anyone for support because, as she says: “I’m used to dealing with things by myself, because nobody believed there was anything wrong with me all these years.”

Helen is one of the most extreme cases and is only able to stay awake with the aid of medication.